The present invention relates to a tennis ball comprising a spherical rubber core and a felt covering affixed thereto, and more particularly to an improvement in the felt covering.
Ordinary tennis balls generally consist of a spherical hollow core having a rubber elasticity and a felt or textile covering affixed onto the core.
For the felt for covering the core, there has been used, for instance, a woven felt called melton which is prepared by satin-weaving a blended yarn of wool and a chemical fiber such as nylon fiber; gigging and milling the satin fabric to form a felt having fibers firmly intertwined to form a dense structure; and a felt prepared by needle punching a fabric.
In general, a woven felt is used for top-grade tennis balls make from the viewpoint of good appearance. The woven felt has been generally prepared from a blended yarn of wool and nylon fiber in a ratio of from 60:40 to 70:30 by weight. It is also proposed to use a polyester or rayon fiber instead of nylon fiber to be blended with wool (e.g. Japanese Patent Publication Kokai No. 60-29157 and Japanese Patent Publication No. 59-135079).
In general, the woven felt is prepared by satin-weaving blended yarns of wool and a chemical fiber such as nylon, polyester or rayon fiber with the use of cotton fiber as under thread, subjecting the satin fabric to raising to form large quantities of raised fibers, and subjecting it to a milling processing peculiar to wool in order to make a raised fiber structure dense by intertwinement of the fibers, thus finishing up the satin fabric into a thick felt of good appearance. Such an intertwinement of the fibers resulting from the milling processing is peculiar to wool, and chemical fibers have no such action.
The felt covering of tennis balls reduces in thickness from being played since the felt fibers are gradually worn away and cut by repeated collision with a tennis court, thus resulting in a worn state. Wool is poor in abrasion resistance. Since a felt covering made of only wool shows marked abrasion by collision with a tennis court, it has been reinforced by blending a chemical fiber, as mentioned above. Nylon 6 and nylon 66 which are superior in tensile strength and dyeability, have been generally used as the chemical fiber for this purpose.
The fineness of the chemical fibers such as nylon used for this purpose is usually 6 deniers. In case of further increasing the abrasion resistance, chemical fibers having a fineness as thick as 12 deniers are used, but the use of 12 denier fibers is not desirable in that, since they are firm, namely bristle-like, it is difficult to sufficiently press down the fibers by milling processing, thus resulting in a rough appearance.
When nylon is used in an amount of 50% by weight or more in order to raise the abrasion resistance, milling effect is decreased, thus the obtained tennis balls show rough appearance, and also the ball characteristics are decreased so as to hinder playing due to marked napping during playing.
The felt covering has a function of decreasing an impact to a player at the time of striking a ball by a racket, and a function of controlling the ball speed by air resistance. These functions are also impaired by wear of the felt. That is to say, the tennis ball in play contacts the surface of a court and rebounds after sliding a short distance. At that time a frictional force generates between the ball and the court, whereby the fibers of the felt surface are gradually worn and cut away to reduce the thickness of the covering. Since the speed of ball struck increases with the increase of wear, the worn ball is no longer used and is exchanged with a new ball for playing. A high wear resistance of the felt covering is desired from an economical point of view.
In recent years, all weather tennis courts easy in maintenance have been popularly used, in addition to conventionally spread clay courts and en-tout-cas courts which do not so wear the felt covering. Various materials such as asphalt-type, polyurethanes and synthetic rubbers are used as the surface materials of all weather tennis courts, and among them some surface materials remarkably wear the felt covering. A high wear resistance of the covering is desired also from this a point of view.
It is a primary object of the present invention to improve the wear resistance of the felt covering of tennis ball while maintaining the good the appearance of the covering which directly affects the appearance of the ball itself and without decreasing a resistance to napping of the covering which occurs at the time of playing.
A further object of the present invention is to provide a tennis ball with a felt covering having an improved wear resistance, a good appearance and a good napping resistance.
These and other objects of the present invention will become apparent from the description hereinafter.